Human embryonic stem cells (hESC) have the potential to provide unlimited supplies of healthy cells for the implementation of regenerative medicine and the reconstitution of diseased organs. Yet, equally significant is their potential for providing insights into fundamental principles and mechanisms guiding early human development. Embryonic stem cells have very specific culture requirements for the maintenance of undifferentiated proliferation and pluripotency, beyond the routine cell culture practices feasible within individual research projects. In addition, assays for their differentiation and modification are tedious and laborious. We propose a new Embryonic Stem Cell Core for this P01 to support studies with hESC. We propose 3 specific aims: Specific Aim 1. To provide undifferentiated hESC for projects //, III, IV and maintain stocks of hESC, conduct routine quality control, and characterize additional lines as necessary. Specific Aim 2. To conduct preparation of embryoid bodies, teratomas and other procedures as needed by individual projects. Specific Aim 3. To train investigators' staff in hESC culture, manipulation, and modification for individual experiments. All of these activities are currently routine in the Pis lab, and their incorporation into this core will provide opportunities for new synergistic studies with trophoblasts and endothelial cells, in support of research in the regulation of angiogenesis at the maternal-fetal interface. It will also ensure consistent standards of resources and practices with these new endeavors.